4-year climatology of global drop size distribution and its seasonal variability observed by spaceborne dual-frequency precipitation radar

This study investigates the global drop size distribution (DSD) of rainfall and its relationship to large-scale precipitation characteristics using the Dual-frequency Precipitation Radar (DPR) onboard the Global Precipitation Measurement (GPM) Core Observatory. This study focuses on seasonal variations in the dominant precipitation systems regarding variations in DSD. A mass-weighted mean diameter (D_m), which is estimated based on the dual-frequency information derived from the GPM/DPR, is statistically analyzed as a typical parameter of the DSD. Values of the annual mean D_m, in general, are larger over land than over the oceans, and the relationship between D_m and precipitation rate (R) is not a simple one-to-one relationship. Furthermore, D_m exhibits statistically significant seasonal variations, specifically over the northwest Pacific Ocean, whereas R shows insignificant variations, indicating the variations in R cannot explain the distinct seasonal changes in D_m. Focusing on the seasonal variation in D_m over the northwest Pacific Ocean, the results indicate that the variation in D_m is related to the seasonal change in the dominant precipitation systems. In the summer over the northwest Pacific Ocean, D_m is related to the organized precipitation systems associated with the Baiu front over the mid-latitudes and tropical disturbances over the subtropical region, with relatively higher precipitation top heights, composed of both stratiform and convective precipitations. Contrary to the summer, larger D_m over the mid-latitudes in winter is related to extra-tropical frontal systems with ice particles in the upper layers, which consists of more stratiform precipitation in the storm track region. The smaller D_m over the subtropical northwest Pacific Ocean in winter is associated with shallow convective precipitation systems with trade-wind cumulus clouds and cumulus congestus under the subtropical high.